Salinity is a major constraint
for rainfed rice production in Northeast Thailand sandy lowlands. Salinity
surveys are currently performed using Electromagnetic Induction method (EMI)
that is associated with soil conductivity measurements. Previous survey methods have
consisted of performing EMI measurements during the dry season with the
assumption that capillarity rise was the main cause of salt excess in the top
layers of the
growing rice. Hydrodynamic studies have demonstrated that in some cases the
main process of salt enrichment of the top layer consists of the ascent of salt water from
the aquifer during the rice cycle. An adaptation of EMI measuring device was
realized in order to allow the surveys to be performed during the flooded period. Measurements in
horizontal and vertical dipole configuration were performed in an area of contrasted salinity, comparing
the obtained values with the conductivity of soil and water mixtures of the top layer.
Measurements during rice flooding period indicated better relationship between
salt contents and vertical dipole measurements than those performed during the dry
season. Salinity in the top layers in the two different stages was identified
with two different processes of spatial distribution: on the one hand,
capillarity rise
during the drying period, and on the other hand the circulation of saline
solutions during the flooded periods. Therefore, EMI measurements during flooded
periods should be recommended in salt-affected sandy paddy soils as more accurate and
representative of conditions that influence plant performance.

Sandy soils of Northeast
Thailand have for long been identified as problematic soils. Acidity, salinity,
low organic
matter contents and low cation exchangeable capacity (CEC) have been
established as the main soil constraints to rice production on these sandy soils. CEC
values are dependent on clay content, soil organic matter content and soil pH. In
the context of sandy salt-affected soils, precise and accurate determinations
of low CEC
values are often considered problematic and a large number of methods are
available to measure this attribute. The objective of the study was to compare the values
obtained on a set of 6 samples using different methods of CEC determination in the context of
salt-affected sandy paddy soils. Ammonium acetate method at pH 7 and
cobalt-hexamine at soil pH methods with or without alcohol pretreatment were
compared with
compulsive method, with CaCl2 at the same pH. In sandy soil paddy
profiles with a low clay content and CEC values measured with compulsive methods, less to 2.67
cmolc kg-1 determinations with ammonium acetate and
cobalti-hexamine
methods presented linear relationships with the compulsive method results in cmolc kg-1(ofsoil)CECcobalt = CECcompulsive*
0.45 + 1.84, R2 = 0.93) and (CEC ammonium= CECcompulsive* 0.37
+ 1.91, R2
= 0.87). The same type of relationships were established performing previous
alcohol treatment in order to remove salts although with lower significance
(respectively R2 = 0.56 and R2 = 0.80). These results
indicate that
using ammonium acetate or cobalt-hexamine methods, in salt-affected sandy soils
with a CEC lower 2.67 cmolc kg-1 will lead to overestimation of CEC
when compared to compulsive method. This overestimation was found to be independent of pH values and
salt-effect.

Highly weathered light-textured
soils with low chemical activity are common in Thailand and provide significant management
constraints. Representative topsoils and subsoils of Kohong, Klong Thom, Sadao,
Tasae, Yasothon, Thai Muang, Chalong, and Hang Chat series have been
investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and chemical
analyses. Clay-sized particles in the soils range from 76 to 207 g kg-1
(median 139 g kg-1). These soils are acid (pH in water 4.0-4.8),
having very low to low organic matter contents (2.4-23.4 g kg-1), low cation
exchange capacity (0.6-4.5 cmolc kg-1), and very small to small values
of specific surface area (SSA) (2-11 m2 g-1). Kaolin
group clay minerals are the major constituents (>70% content) of the clay
fraction, with minor amounts of inhibited vermiculite, illite, quartz, and
anatase. Goethite is present in most of the soils with hematite in Sadao series
(Typic Kandiudults). These soil kaolins exhibit a wide range of crystal sizes ranging
between 0.06 to 0.83 µm, and most of the crystals are very small, euhedral, hexagonal platy. They contribute most of the
CEC of these soils.

The Fed concentrations
in these soils (4-12 g kg-1) are much higher than Feo
concentrations (0.2-1.6 g kg-1) with the values of Feo /Fed
ranging from 0.05 to 0.23 (median 0.12) indicating that most of the free iron oxides are crystalline which is
consistent with XRD measurements. Amounts of Ald and Alo
are about equal with median values of 0.7 and 0.4 g kg-1, respectively.
These oxide constituents are important for the retention of anionic plant nutrients.

We consider that the small
amounts of clay-sized materials in these soils play a vital role in plant
nutrient retention
and the soils should be managed conservatively to protect these materials.

1 Office of Science for Land
Development, Land Development Department, Chatuchak, Bangkok 10900, Thailand.2 Department of Soil Science,
Kasetsart University, Bangkok 10900, Thailand.3 School of Earth and
Geographical Science, Faculty of Natural and Agricultural Science, University
of Western Australia,
Crawley, WA 6009, Australia.

Sandy soils which are very common
in Northeast Thailand have the capacity to adsorb different amounts of phosphate. This study was
undertaken to determine the amount of adsorbed phosphate released from five
sandy soils from the region. Adsorption was first carried out by shaking
samples of each soil for 30 minutes, twice daily for 6 day, with 0.01 M CaCl2
solution containing phosphate in a concentration range from 1 to 32 mg P L-1.
Desorption isotherms were determined in a similar manner by re-shaking the wet
samples and their adsorbed phosphate with calcium chloride solution using a
soil:solution ratio of 1:10. Measurements suggest that phosphate sorption for all soils were
almost irreversible. The adsorption and desorption isotherms of all soils conformed to the
Langmuir equation. The adsorption maximum value was used to determine the phosphate saturation. Desorption
of adsorbed phosphate increased with increasing saturation percentage. Average desorbability at low
saturation (<20%) and high saturation (>80%) was 0.5 and 12%
respectively. Dithionite – citrate – bicarbonate and oxalate extractable iron
were the major phosphate adsorbents in the study.

Poorly fertile sandy soils are
widespread in Northeast Thailand. This represents a serious threat to local
farmers and constrains economic development in the region. Here, we evaluate
the fertility of these soils. We studied the physico-chemical and mineralogical properties
of five pedons along a transect located at 25 km Southwest of Khon Kaen,
respectively under forest (F), sugarcane (SC) and in paddy fields (PF1, PF2,
PF3). All soils have a very low organic matter content (<1%). They differ in
weathering stage and mineral reserve. The well drained soils under the F and SC
are more weathered than the poorly drained PF profiles. Kaolinite is the major phyllosilicate in F
and SC, whereas smectite is the dominant clay mineral in PFs. In the
toposequence, the total content
of major alkaline and alkaline-earth cations (TRB), i.e. mineral reserve, is confined to the clay fraction
(<2 µm). From PFs to SC and F, it decreases with decreasing CEC and total Mg
content, as
well as with the disappearance of smectite and the appearance of 1:1-2:1 mixed
layered clay minerals.
In addition, KCl-extractable Al becomes the major cation on the effective CEC
in the well drained soil profiles. We propose that clay minerals act here as key
proton-consumers. As such, smectite dissolution is supported by a high content of
exchangeable Mg relatively to Ca, and by the XRD detection of 1:1-2:1 interstratified clays. Such clay
minerals represent, indeed, an intermediate stage in the processes of smectite dissolution and kaolinite
formation in low silica and freely drained soil environments. The conservation
of the clay
exchanger must be a key objective in the management and use of these poor sandy
soils. In addition, in situ soil monitoring is required to further assess the dissolution of 2:1
clay minerals and the proposed corresponding
Mg-depletion.

A study on the potential of
Quartzipsamments to support the growing of sugarcane on the Southeast Coast,
Thailand was undertaken on four representative soil areas. The methodology used
in this study included pedon analysis of soils in the selected areas, laboratory
analyses of their physico-chemical properties, mineralogy, micromorphological
characteristics and assessment of their properties related to sugarcane crop
requirements.

Results of the study revealed
that these soils are Quartzipsamments deposited on the coastal plain. They are deep soils developed mainly on local alluvium and
wash deposits derived from granite. Their micromorphological
characteristics show subangular to subrounded quartz grains as the major fabric
component. Their texture ranges from
sand to loamy sand and their bulk density ranges from moderately low to high (1.40-1.82 Mg m-3). Chemical
analysis of soils indicates that they have a strong acid to neutral reaction (pH 5.1-6.8). They have very low to low organic
matter contents (0.2-9.4 g kg-1), very low total nitrogen (0.01-0.03 g kg-1), very low to high
available phosphorus (1-95 mg kg-1) and very low to low available potassium (1.5-46.8 mg kg-1). The soils
have very low to medium cation exchange capacity (2-11 cmolc kg-1).
Their base saturation percentage varies widely from 4-77%. Their
electrical conductivity ranges from 0.1-1.9 dS m-1 indicating no
salt-effect.

Fertility assessment results
indicate that most of these sugarcane-growing soils have low fertility except for a single area where the soil
has a moderate fertility status. Their potential based on suitability
assessment indicates
that most of them are moderately suited but one profile is not suited for
sugarcane growing because of its sandy texture and strongly acid condition. A
recommended approach to increase their potential for sugarcane growing includes an emphasis on soil organic
matter conservation and a more intensive soil-fertilizer
management. A continuing effort on soil-fertilizer management is clearly needed
to maintain effectiveness in sugarcane growing on these soils.

The present paper is part of a comprehensive approach
currently developed in Brazil to study biogeochemical
cycles at the ecosystem level in Eucalyptus grandis plantations. It aims
at assessing changes occurring in
water chemical composition throughout their transfer in the soil, during the
first year after planting. A
lysimetry was installed in a 5-year-old E. saligna stand. Lysimeters
were strategically positioned within
a compartment of E. saligna prior to the clear felling of the stand that
would allow the assessment of a fertilization experiment planned on the same
site for the next rotation. About 180 zero-tension lysimeters were installed in the upper soil layers and 136
ceramic cups were setup horizontally down to a 3 m depth and connected to an automatic vacuum pump. After the
harvest of the E. saligna stand, a fertilization experiment of E.
grandis improved seedlings was initiated using a complete randomized block
design, with 6 blocks and 5 treatments. The
objective was to compare the influence of different amounts of ammonium
sulphate and sewage sludge fertilizations on biogeochemical cycling. At the end
of the rotation, nutrient concentrations in soil solutions were low whatever
the depth and the lysimeter type. After clear felling, soil solution ionic balances were dominated by NO3-
and Al3+, whose concentrations increased substantially. No obvious change in concentrations was observed for
all other elements. A proton unbalance, resulting from the interruption of NO3- uptake
by plants after harvesting, might be responsible for the aluminium accumulation
in soil solutions. After planting,
fertilizer inputs were responsible for increasing concentrations of all
elements applied until 1 m deep. Twelve
months after planting E. grandis, the chemistry of soil solutions at 3 m
deep had not developed. The monitoring of soil solution chemistry is going on
in order to quantify the effects of these different fertilizations on
deep drainage nutrient losses.

Introduction

Fast growing Eucalyptus plantations cover approximately 3 millions hectares in Brazil. This
sector is of great economical
importance since the Eucalyptus-plantation production supplies the Brazilian cellulose and paper industry as well as the
metallurgy industry through the
production of vegetal charcoal. Due
to several decades of research, the productivity of these plantations
now ranges from 30 to 50 kg ha-1 year-1 according to soil
characteristics and water availability (Gonçalves et al., 2004).

The ecological impact of Eucalyptus
plantations has been widely discussed around the world (Cossalter and Pye-Smith, 2003). In
particular, water consumption by eucalypt stands has been extensively investigated. But few studies have ever
assessed the influence of silviculture on
superficial water chemistry. Such studies
are nonetheless necessary to identify and foster practices minimizing the silvicultural impact on the water table chemistry of afforested catchments.

A comprehensive approach is
currently being conducted
at the University of São Paulo to study the biogeochemical cycles of nutrients in Eucalyptus grandis plantations. This project is developed at the ecosystem level in an experimental stand
representative of large areas of
plantations in Brazil. The overall aim of the study is to assess the
consequences of silviculture, and more
particular of different fertilizer inputs, on water quality and long-term soil
fertility by measuring water and
nutrient fluxes throughout the ecosystem. The present paper focuses on
changes occurring in soil solution chemical
composition during the first year after planting.

Materials and methods

Site characteristics

The study was conducted at the
ESALQ/USP experimental
station of Itatinga (23º02′S, 48º38′W). The annual mean precipitation is 1,300 mm and the annual mean temperature is 20ºC.
Figure 1 shows the time course of
rainfall and temperature over the sampling
period. The selected site is representative of the typical relief of the São Paulo Western Plateau. The maximum altitude of the area is 863 m. The slopes
are flat to undulating (3%) in the
experimental stand. The lithology is composed of sands, Marilia
formation, Bauru group. The soils are “Latossolos Vermelho-Amarelo” according to Brazilian classification.
Soil analysis showed that sand
content was >75%, whatever the soil layer, down to >6 m.

Figure 1. Time
course of average temperature (ºC) and total precipitation (mm) at the
experimental site

The Itatinga experimental station has been covered for
60 years with Eucalyptus saligna plantations.
These stands were first planted in 1945 on pasture and have been managed
in short rotation coppices for fire wood production since then. The
experimental design was implemented in 2003 in a 6 ha coppice harvested in 1997, and planted in 1998 with Eucalyptus saligna. Tree spacing was 3
m X 2 m and only a NPK (10:20:10) starter fertilization of 300 kg
ha-1 was applied.

Methodology

A lysimetric design was installed at the beginning of 2003 in the 5-year-old E. saligna.
Lysi-meters were positioned appropriately for a fertilization experiment
planned on the same site for the next rotation,
after the harvest. A 3 months period was left for soil stabilization,
and then nutrient fluxes were monitored over a 9 month period prior to the harvesting of the stand (from July 2003 to
February 2004). In February 2004,
the stand was clear felled and the stumps killed using glyphosate.
Improved E. grandis seedlings were planted on the same planting rows at half-distance between the stamps, without
any soil preparation. The previous
stocking density was maintained (2 m × 3 m spacing).

A nitrogen fertilization experiment was then initiated using a complete randomized block
design, with 6 blocks, 5 treatments
and 100 trees per plot. The fertilization treatments imposed were those
classically used by Brazilian
companies on these soil types: all mineral
fertilizers but N (T1) (Control), all mineral fertilizers (T3), and sewage sludge fertilization (T5). Nutrient
fluxes were measured in these three treatments
(T1, T3, T5) in blocks 1, 2 and 3. Blocks 4, 5
and 6 were installed to sample trees
at various ages without disturbing
the lysimetry design (Table 1). T2 and T4
treatments were installed to help establish a
response curve to N inputs. The fertilizations applied in each treatment are presented in Table 1.

The soil solution sampling equipment was installed in blocks 1, 2 and 3 of treatments T1,
T3, T5 according
to a systematic constant scheme. Throughfall solutions were collected from 12
funnels systematically located beneath the trees in each one of the 9 experimental plots. In each plot, 3 sets of 9
narrow zero-tension lysimeters (40 × 2.5
cm) were installed beneath the forest floor, and zero-tension plate lysimeters (50 x 40 cm) were introduced at 15, 50 and 100 cm deep (5 at each depth) from pits backfilled
after installation with the horizons in their natural arrangement. The
litter and soil solutions were collected in
polyethylene containers situated downhill in closed pits. Moreover, 4
replicates of tension lysimeters were
installed horizontally at the depths of 15 cm, 50 cm, 1 m, and 3 m in each plot. They were connected to a
vacuum pump and automatically maintained at
a constant suction of -70 kPa. Ceramic-cup solutions were collected in
glass bottles. All lysimeters were set up representatively near and between the
trees to take into account spatial variability.
In each plot, lysimeters of same type and depth were connected to one
collector in order to reduce the number of chemical analyses. Chemical
analyses of solutions collected by each ceramic cup separately were performed in a
few blocks and depths in order to
estimate the spatial variability (data not presented).
Rainfall solutions were collected in a 1 ha opened area, next to the
experimental plots.

Table 1. Experimental treatments and fertilization
strategies imposed

Nitrogenous
fertilization

Other fertilizers

Amount

Fertilizer type

Application
type

Control

T1

0

4 equal partsat planting

Triple superphosphate (75 kg ha-1 P2O5)

KCl (30 kg ha-1)

Trace elements (45 kg ha-1 FTE BR12)

Boron (45 kg ha-1 Borogran)

Dolomitic limestone (2 t ha-1)

T2

40 kg ha-1

Ammonium sulfate

6 months

T3

120 kg ha-1(commercial fertilization)

12 months

T4

360 kg ha-1

18 months

T5

350 kg ha-1 Ntotal

10 t ha-1 sewage
sludge (Barueri, SP)

2 equal parts at planting at 8 months

KCl (30 kg ha-1 K2O)

Solutions were collected each
week from July 2003 to June 2005. A composite sample for each type of collectorwas prepared every 4
weeks. The solutions were filtered (0.45 µm)
and the pH was measured. SO42-,
NO3-, NH4+, Cl-, H2PO4-,
K+, Ca2+, Mg2+, Na+ were analysed by chromatography (Dionex). Al, Fe,
Si and dissolved organic carbon (DOC)
were determined by ICP and Shimadzu equipment for each depth, treatment
and collector type on a three-block composite sample.

Soil solution ionic balances were computed considering the species: SO42-,
NO3-, NH4+, Cl-, H2PO4,
K+, Ca2+, Mg2+,
Na+, H+. NO2 and Fe concentrations were
very low so that they were neglected in the calculations.
As the pH of soil solutions were between 4 and 5 until 1 m deep, aluminium was considered as Al3+
in this first preliminary approach.

The whole study will help to relate the soil solution characteristics to the dynamics of
biomass and nutrient accumulation in the stands, as well as of nutrient returns to the soil with litter fall and
forest floor decomposition.

Results and discussion

Nutrient concentrations in soil
solutions were low
(<100 µmolc
L-1) over the 9 months of monitoring at the end of stand rotation, whatever the depth
and the type of lysimeter (Laclau et al.,
2004). A similar behaviour was observed in other tropical forest plantations. This confirms the species ability to
prevent deep drainage nutrient losses as soon as the root system is completely
developed (Lilienfein et al., 2000; Laclau et al., 2003a).

Clear felling sharply increased nitrate con­centrations in surface (0-50 cm) soil layer solutions, and this, without any fertilizer application
(Figure 2). This pattern suggests
that the sudden interruption of N uptake by plants resulting from herbicide
application, combined with the
production of mineral N by the mineralization of soil organic matter and
forest residues, led to an accumulation of
mineral N in these soil layers.

Soil solution ionic balances were
dominated by NO3-
and Al3+, and the concentrations of other elements were little influenced by clear
felling during the first months (data not shown). The accumulation of NO3-
in soil solutions
was thus linked with the release of Al3+ in soil solutions. The
hypothesis formulated to explain such behaviour was that the interruption of NO3-
uptake by plants
leaded to a proton unbalance which might be responsible for the accumulation of aluminium in soil solutions. Indeed, after clear felling, the protons released during the nitrification were no more
removed from soil solutions by plant anion uptake and thus, accumulated in the soil solution (Van Breemen et
al., 1984). The H+ may
then have desorbed the Al3+ on the ion-exchange sites and solid phase dissolution, leading to an
increase of aluminium concentrations in soil solutions.
As an increase of Si concentration in soil solutions was also observed after clear cutting, some mineral weathering may also have occurred under H+
influence, releasing mineral Si and Al in soil solutions.

After the planting, fertilizer inputs were responsible
for an increase in surface layer concentrations
in all elements applied (K+, Cl-, NH4+,
SO42-, Ca2+,
Mg2+). It resulted in increasing sums of cations and anions as well as the predominance of
the elements brought by fertilization in the ionic balance, as for NH4,
Mg and Ca regarding cations (Figure 3). The sum of cations was then very high (>7,000 µmolc L-1)
but declined with depth and time until reaching more common values at 3 m deep. At this depth, the
sum of cations was
approximately 200 µmolc L-1, that is,
of the same order of magnitude of total cationic concentrations observed before clear felling and confirms previous
observations under Eucalyptus plantations
in the Congo (Laclau et al., 2003a). These values confirm the nutrient poorness of these sandy soils. In comparison, total cationic charges
reported in solutions collected in
undisturbed Eucalyptus native forests
in Australia were about 1,000 µmolc L-1 (Adams and Attiwill, 1991; Attiwill et al., 1996) as in most
studies in temperate forest ecosystems (e.g.
Beier and Hansen, 1992; De Vries et al.,
1995; Cortez, 1996; Marques and Ranger, 1997).

In the case of aluminium and nitrates, this enrichment was cumulated in treatments T3
and T5 to the first
accumulation mentioned above (resulting from herbicide application). During the winter 2004, nitrate concentrations reached 80 mg L-1 in
the top soil (15 cm deep, solutions sampled by ceramic-cup lysimeters). After September 2004, the
rainfall events led to a decrease in nitrate concentrations at 15 cm deep. Nitrates were then leached to deeper soil layers,
as well as uptaken by tree roots to
support the growth. The nitrate concentration peaked at 50 cm deep from
September 2004 to February 2005, where it reached 95 mg L-1 in T5. It reached
the depth of 100 cm from January to May 2005 where it ranged up to 60 mg L-1 in T3 and T5 (Figure 2). Fifteen
months after clear felling the E. saligna
stand and twelve months after planting E. grandis, the soil
solution chemistry of deeper layers (300 cm
deep) had not been modified. Soil moisture sensors (TDR) installed in
the experiment showed that preferential
drainage were not the dominant transfer process in this sandy soil, which was
consistent with the time course of NO3-concentrations at
3 m deep.

Moreover, soil solution
concentrations can be compared
to nutrient uptake by the trees. At 1 year of age, the total dry biomass (above and
below-ground) of the
stands were 9,380, 12,430 and 10,920 kg ha-1 in treatments T1, T3
and T5, respectively (Laclau et al., 2005). The amount of nutrients taken up from the soil during the first year of growth ranged from
70 to 104 kg N ha-1, 4 to
9 kg P ha-1, 31 to 46 kg K ha-1, 31 to 45 kg Ca ha-1, 10 to 17 kg Mg ha-1,
according to treatment. A sharp
increase in Leaf Area Index (LAI) was
observed during the first rainy season (LAI ranged from 0.4 to 0.7 at age 6 months and from 2.0 to
2.7 at age 1 year). During the second
year of growth, the tree uptake should considerably increase: at the end of the
first year of growth, the root system had already reached 3 m deep, and
during the second year of growth stand
nutrient requirements will be maximal (Laclau
et al., 2003b). Moreover, evapo-transpiration is expected to increase in this stand until canopy closure at age 2
years. The drainage flux should then considerably
decrease until 3 m deep during the second year of growth. Beyond 3 m
deep, soil moisture sensors (TDR) installed
in this experiment will make it possible
to quantify the drainage fluxes and therefore the losses of nutrients. These losses are expected to be low
since during the first year of growth the soil solution enrichment had not reach 3 m yet, and since as seen
before, the nutrient uptake by the trees is expected
to increase significantly during the second year of growth.

Conclusion

The biogeochemical cycling study
in progress in this Brazilian eucalypt
plantation showed a clear influence of
clear felling on nitrate and aluminium. Despite high rainfall amounts, one year after planting, they had not reached the depth of 3 m yet. This
pattern, as well as TDR sensors
installed in the experiment, suggests
that preferential drainage was negligible in this sandy soil. The
monitoring of soil solution chemistry will
go on during the second year of growth.

This study is expected
to assess whether the fast development of
eucalypt root system and the high nutrient requirements of the early growth
make it possible to avoid large nutrient losses by deep drainage, despite the
relatively high amounts of fertilizers applied.

Acknowledgements

We thank the São Paulo Research Support Foundation FAPESP (Project 02/11827-9) for
providing financial support.

In recent years, atmospheric
composition of greenhouse gases has been changing rapidly. Since methane (CH4) is continuing to
increase its concentration faster than other greenhouse gases such as carbon
dioxide (CO2) and nitrous oxide (N2O), methane attracts
attention internationally as an important greenhouse gas. The paddy field occupies one of
major sources of the methane. In this r esearch, production potential of the greenhouse gases in tropical
saline sandy paddy soil was investigated and the influences of fertilization
and methods of crop establishment on these gases fluxes were also examined in
tropical saline sandy paddy fields. The soil samples were collected from three paddy fields
(Ban Kota, Ban Don Do, Ban Kham Pia) in Khon Kaen, Thailand and used inr
laboratory incubation experiments to measure CH4 and CO2
product potential, mineral N, soluble organic carbon and ferrous iron changes
during the incubation. Mor eover, we measured greenhouse gas fluxes by the
closed-chamber method in Ban Kota paddy field. Methane production varied widely among soils, but similar
trends were observed with CO2 production, although not as other
parameters. Methane
and CO2 emissions were higher from broadcasted rice crops when
compare with transplanted plots but no obvious difference was found between organic and
chemical fertilization treatments.